GtTLF OF MEXICO COMMERCIAL SHRIMP POPULATIONS 



349 



ordinarily of 1 to 5 days' duiiitioii, trips from 

 United States ports to the distant C'ainpeche 

 grounds occasionally cover a 7-weck. period. In 

 the latter situation, vessels may transship their 

 catches on others periodically departing for home 

 port and then continue to fish until they, too, 

 leave the fishing grounds at the end of the period 

 indicated. Depending on the species sought, only 

 a relatively small proportion of the time away 

 from port may be spent in actual fisiiing. 



Routine operating procedure is to fisii the main 

 net or nets for IJi- to 5-hour periods depending on 

 the density of shrimp. When shrimp exliibit 

 patchy distribution and are scarce, the "try" net 

 is fished continuously for 20- or 30-niinute periods 

 until its catcli indicates that profitable quantities 

 are available. Searching may frequently extend 

 over as much as 5 days before the main nets are 

 lowered into paying concentrations of market-size 

 shrimp. 



Most offshore fishing is at night, reflecting 

 nocturnal activity of brown and pink shrimp 

 which greatly increases their availability. An 

 average night's fishing for these species covers 

 about 10 hours during which time the nets are 

 hauled two to five times, the mean being about 

 three. White shrimp are generally fished during 

 daylight hours, though in certain seasons they may 

 be taken at night along with brown shrimp. 



Catches are sorted and iced immediately or soon 

 after removal from the net. If individual shrimp 

 are large and not too numerous, they are beheaded 

 prior to icing. In all other instances, heads remain 

 intact until final processing ashore (fig. 5). Dis- 

 cards of undersized shrimp may be substantial 

 at certain seasons, but accurate measures of their 

 magnitude for any season or area have never been 

 obtained. 



More specific details of shrimp fishing and 

 processing operations maj- be found in U.S. Fish 

 and Wildlife Service (1958). 



COMMERCIAL FISHERY STATISTICS 



Accurate statistics of trawling operations and 

 shrimp production in the Gulf of Mexico were not 

 maintained prior to 1956. In that year a Gulf- 

 wide statistical survey was inaugurated to provide 

 a continuous flow of data that would facilitate 

 studies of fishery economy and biology. It has 

 since functioned with no major changes. 



From the outset, however, survey resources 

 permitted full statistical coverage only of that 

 fishery centering on the conuncrcial utilization of 

 shrimp for human consumption. Operations and 

 production in noncommercial and commercial 

 bait fisheries have gone largely unrecorded. As a 

 consequence, available statistics give an incom- 

 plete picture of total shrimp harvest in the Gulf 

 coast area, and allow appraisal of only those 

 portions of populations supporting what was 

 defined earlier as the "commercial" fishery. 



In studies using data obtained from sources such 

 as the present survey, a review of survey design 

 and techniques helps to place in proper perspective 

 interpretations of analyses to whicii resulting data 

 may be subjected. 



DISTRIBUTION OF SURVEY PERSONNEL 



Sixteen "statistical" or "port" agents record the 

 daj'-to-day operations and production of tlie 

 United States commercial shrimp fleet. Strate- 

 gically located at landing ports around the Gulf — 

 four in Florida, one each in Alabama and 

 Mississippi, and five each in Louisiana and Texas — 

 they canvass fishermen and processors for detailed 

 information on location and amount of fishing, 

 volume and composition of shrimp landings, and 

 current marketing conditions, relaying it after 

 necessary adjustment to Washington, D.C., for 

 final processing. This consists of asscml)ling the 

 data on a monthly basis and publishing them in 

 tables entitled "Gulf Coast Shrimp Catch bj* -;Vrea, 

 Depth, Variety, and Size." 



IDENTIFICATION OF FISHING GROUNDS 



To facilitate geographical assignment of com- 

 mercial trawling effort and hence classification of 

 shrimp landings as to origin, the continental shelf 

 of the Gidf of Mexico has been subdivided coast- 

 wise into 40 statistical subareas (fig. 6). Num- 

 bered counterclockwise beginning off the Florida 

 Keys, these have been further subdivided from the 

 shoreline to 45 fathoms into three deptii zones, and 

 grouped into eight coastal areas. Bottom areas 

 for each statistical unit are given in table 1. 



DISTRIBUTION AND AMOUNT OF FISHING EFFORT 



One of two important variables involved in 

 measuring ilemersal populations is the time spent 

 trawling, referred to herein as fishing effort. It 

 was and continues to be estimated bv means of 



